(1) Field of the Invention
The present invention relates to the ice protection of aerodynamic surfaces. In principle the invention may be applicable to the protection of any form of aerodynamic surface which is liable to encounter icing conditions in service, including in particular the surfaces of aircraft wings, propellers, stabilisers, fins, engine nacelles and radomes, helicopter rotor blades and wind energy turbine blades.
(2) Description of the Art
As is well known, ice accretion can occur on an aerodynamic surface when subject to an airflow containing airborne water at a temperature below or near its freezing point. The uncontrolled build up of ice on such surfaces is undesirable for many reasons, including the additional weight which must be carried, reduction of the aerodynamic efficiency of the surface, the imposition of out of balance loads on the structure, and the danger to other structures or persons from uncontrolled shedding of the ice. Many forms of ice protection systems for such surfaces are therefore already known, one large class of which comprises electrothermal means where electrical resistance heating elements, for example in the form of wires, foils, sprayed metal matrices or conductive fabrics, are used to raise or maintain the temperature of the surface above the local freezing point. Within the nomenclature of electrothermal ice protection systems “anti-icing” refers to the process of maintaining a surface at a temperature above freezing point over a continuous period of time so that ice is prevented from forming, while “de-icing” refers to the process of permitting a certain limited amount of ice to build up on a surface and periodically removing it by heating the surface at selected intervals. The present invention seeks to provide a form of electrothermal ice protection system which is adaptable to use with a wide variety of aerodynamic surfaces and may offer significant manufacturing cost advantages in comparison with systems currently in service.